Allergenicity of milk proteins

Food allergy affects around 3.5 per cent of the general population and 7 to 8 per cent of children. Milk allergy mainly affects young children, most of whom outgrow it spontaneously by the age of 3. The components responsible for the allergy are proteins. No specific structure or function is solely responsible for, or even directly associated with, allergenicity, which is not an intrinsic property of the protein. Most milk proteins are potential allergens, even those present in very low concentrations. The structures responsible for allergenicity are epitopes, which may be conformational or linear. They are numerous, varied and distributed across almost the entire protein molecule. Linear or sequential epitopes are of significant clinical importance as they serve as good markers of persistent and severe allergies. They may consist of short peptide fragments, buried within hydrophobic regions of the protein, which contain highly conserved sequences showing strong homology with the milk proteins of other mammals; these are responsible for the cross-reactions observed in allergic patients. However, a new form of allergy to goat’s or sheep’s milk, without any associated allergy to cow’s milk, is being observed with increasing frequency. The variability and heterogeneity of immune responses in allergic individuals make it impossible to predict the impact of technological processing on the allergenicity of a protein or a fragment or compound derived from it. Furthermore, there are no reliable data available to establish thresholds below which milk consumption would be insufficient to trigger an allergic reaction in sensitised individuals.